Iron chlorosis

Raspberries grown in heavy soils or soils with a high pH will often have yellow or white leaves with green veins. The lack of chlorophyll is called chlorosis. When the chlorosis is caused by an iron deficiency, the disorder is called iron chlorosis. With iron chlorosis, the lightest colored leaves are always the youngest leaves, which in raspberries are at the tips of the primocanes (first year canes).

Iron chlorosis is caused by a deficiency of the nutrient iron. Without iron, the plant cannot manufacture chlorophyll, and without chlorophyll, the leaves cannot turn green. Iron chlorosis usually grows worse as the plant grows taller. The oldest leaves usually stay green, while the youngest leaves become lighter in color towards the tips of the canes. Unlike glyphosate injury or virus diseases, iron chlorosis rarely deforms the leaves. When the deficiency first shows up, the chlorotic leaves still have the same size and shape as green leaves lower down the cane. With severe iron chlorosis, the leaves will be smaller than healthy leaves, but will still retain a normal shape

Iron chlorosis often occurs in small sections of a raspberry patch. Iron deficiencies are most common in soils with a pH higher than 7.4, and are more likely to occur in clay soils than in sandy soils. Flooding can also cause temporary iron deficiencies. Soils surrounded by concrete can also have a high enough pH for iron chlorosis to occur. In Minnesota, iron chlorosis is most common in the western part of the state, where heavy soils with a high pH are common.

The fastest way to alleviate iron chlorosis is to spray the plants with chelated iron. Chelated iron is iron that has been combined with a type of sugar. The sugar helps the plant absorb iron. With most cases of iron chlorosis, chelated iron only needs to be sprayed once in May or June when the canes first show symptoms. Iron sprays can be found at many garden centers.

If chelated iron sprays do not cure the chlorosis, or if the patch requires multiple sprays, then the patch should either be moved, or the soil amended. Before planting, take a soil test to determine if the pH needs to be amended prior to planting. The best way to amend the soil is to mix acidic peat into the planting hole. The acidic peat both lowers the pH and improves drainage, which will alleviate iron deficiencies.